1. Field of the Invention
The present invention relates to the production of ethylene. In particular, the present invention relates to the production of ethylene which is substantially free of acetylene.
Specifically, the present invention is directed to minimizing contamination of ethylene by acetylene produced by steam cracking. To this end, the present invention is directed to selective acetylene hydrogenation over a palladium catalyst wherein a moderator selected from the group consisting of arsine and phosphine is added as an acetylene converter moderator.
2. Discussion of Background Information
It is generally known that high levels of arsine tend to poison acetylene converter catalysts.
For example, U.S. Pat. No. 4,227,025, MONTGOMERY, is directed to a process for the removal of acetylene from cracked gases obtained from conversion processes in which crude oil containing minor amounts of arsenic are thermally or catalytically cracked, hydrocracked, or otherwise subjected to modification resulting in the production of gases containing arsenic. More specifically, U.S. Pat. No. 4,227,025 discloses that arsenic-poisoned palladium catalysts may be regenerated in place by providing a purging step with an arsenic-free gas under acetylene removal conditions into contact with the hydrogenation catalyst, for example, a noble metal catalyst, such as palladium, until the activity and selectivity for removal of acetylene has been restored to the catalyst.
It is also known to hydrogenate acetylenes using homogeneous catalysts that involve phosphine or arsine ligands.
U.S. Pat. No. 2,268,454, ALLIED CHEMICAL CORP., discloses that complexes of anionic group VIII metal (first or second transition series), and hybrid complexes having 1-3 ligands per metal atom, are useful as catalysts in the homogenous hydrogenation of aldehydes, ketones, olefins and alkynes.
U.S. Pat. No. 4,645,849, GENERAL ELECTRIC CO., is directed to the hydrogenation of unsaturated hydrocarbons compounds using cyclo-metallated ruthenium and known transition metal catalysts to provide high conversion rates.
U.S. Pat. No. 3,574,716, IMPERIAL CHEMICAL INDUSTRIES, LTD., is directed to the hydrogenation of an olefin, acetylene, aldehyde, or ketone carried out in the presence of an iridium trihydride complex with 2-3 moles of trihydrocarbon phosphine, -arsine, or stibine, or trihydrocarbon phosphite, arsenite, or antimonite.
British Patent No. 1,121,643, IMPERIAL CHEMICAL INDUSTRIES, LTD., is directed to hydrogenating olefinically or acetylenically unsaturated compounds in the liquid phase in a solution of rhodium complex containing rhodium, anion, and a triorganoarsine, -stibine, or -phosphine, in a 1:1 to 1:4 mole ratio.
British Patent No. 1,154,937, IMPERIAL CHEMICAL INDUSTRIES, LTD., is directed to hydrogenating an unsaturated organic substrate in an homogenous liquid medium in the presence of a zerovalent platinum or palladium compound containing one or more organophosphines.
U.S. Pat. No. 3,463,830, IMPERIAL CHEMICAL INDUSTRIES, LTD., is directed to hydrogenating an unsaturated hydrocarbon in an inert homogenous liquid medium containing a zerovalent platinum or palladium compound having organo-phosphine ligands.
British Patent No. 1,285,871, IMPERIAL CHEMICAL INDUSTRIES, LTD., discloses the use of tetrahydridoaluminates of group IVA or VIII transition metals in which at least one anionic ligand AlH.sub.4 is bound to the metal, together with further ligands as are required to satisfy valence and coordination requirements as catalysts, in a wide variety of organic reactions including hydrogenation, polymerization and olefin isomerization, and that such catalysts are particularly useful in catalyzing the hydrogenation of olefins and acetylenes under ambient conditions.
British Patent No. 1,182,353, MONTECATINI EDISON S.p.A., discloses that cobalt hydrocarbonyls are useful as active hydrogenation catalysts for hydrogenation of saturated and unsaturated aldehydes, ketones, alkenes, and alkynes in hydrocarbon solutions.
U.S. Pat. No. 3,453,302, MONTECATINI EDISON S.p.A., discloses that trialkylphosphine-cobalt hydrocarbonyls are useful as catalysts in the hydrogenation of alkenes, alkynes, ketones and aldehydes.
U.S. Pat. No. 3,697,615, PHILLIPS PETROLEUM CO., discloses that olefin or acetylene may be hydrogenated in the presence of a mixture of (a) a rhodium or iridium halide complex, and (b) an Al or B halide compound, wherein the complex suitable for this purpose may be bis(triphenylphosphine)- or bis(trimethylarsine) carbonylchororhodium with a co-catalyst being AlCl.sub.3 BI.sub.3, or EtAlCl.sub.2.
French Patent No. 2,588,197, POUDRES & EXPLOSIFS, discloses a catalyst for the hydrogenation of ethylenic or acetylenic bonds which comprises a coordination metallic complex of which at least one ligand is a tert phosphine.
European Patent No. EP-66-287, WACKER CHEMIE GmbH, discloses that catalysts containing, for example, tris(tert.butyl) phosphine, are active catalysts for hydrogenation of C--C double and triple bonds.
British Patent No. 2,171,719, is directed to the hydrogenation of alkynes to alkenes.
U.S. Pat. No. 3,917,737 discloses the hydrogenation of various unsaturated hydrocarbons, including acetylenes, with complexes of FeCo or Ni catalysts carried on oxide supports, which are typically silica-alumina, wherein the complexes normally include phosphine or donor ligands.
British Patent No. 1,378,747 uses silica-supported noble metal complexes as hydrogenation catalysts for various types of unsaturation, including acetylenes.
Thus, the use of phosphines and arsines in complexes used for hydrogenation appear to be generally known inasmuch as ligands confer essential stability on the complex.
U.S. Pat. No. 4,377,503, DESSAU, is directed to a shape-selective zeolitic catalyst useful for various purposes, including hydrogenation of acetylenes. DESSAU discloses that shape-selective characteristics can be imparted to the metal containing catalysts by reducing a metal containing zeolite in the presence of one or more unsaturated compounds; and that selectivity can be increased, for example, by means of high temperature hydrogen treatment of the zeolite. Shape selectivity of the catalyst can be increased by selectively poisoning the catalyst with a "bulky" poison, such as tri-p-tolylphosphine, which is described as being larger than the pore size of the zeolite, and thus deactivates the metallic catalyst component on the "outside" of the catalyst composite to a greater extent than such poisons would poison the metal function in the interstices of the composite.
In general, however, arsine is considered to be a poison for catalysts used in selective hydrogenation of acetylenes.
As indicated above, U.S. Pat. No. 4,227,025, PHILLIPS PETROLEUM CO., is directed to the removal of acetylene from ethylene using catalysts which are periodically reactivated after being poisoned by the arsenic.
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U.S. Pat. No. 4,605,812, PHILLIPS PETROLEUM CO., also directed to removing arsenic impurities, such as hydrocarbyl arsines, from hydrocarbon streams in order to remove the arsine impurities from the hydrocarbon stream effluent with a noble metal hydrogenation catalyst to hydrogenate the olefin present therein.
U.S. Pat. No. 4,593,148, PHILLIPS PETROLEUM CO., is directed to the removal of arsine from gases, for example, by contacting with sorbent comprising copper oxide and zinc oxide, to remove arsine impurities for the purpose of preventing catalyst poisoning by AsH.sub.3 and/or hydrocarbyl arsines in a hydrocarbon feedstream, for example, C.sub.2-6 olefin streams, prior to hydrogenation of acetylenic impurities on noble metal catalysts.
An MDA analyzer model 7100 supplied commercially by MDA Scientific, Lincolnshire, Ill., is a continuous toxic gas monitor which, in the Serials 7100, is disclosed as being useful for ammonia, chlorine, diisocyanates, hydrazines, hydrides, hydrogen chloride, hydrogen cyanide, hydrogen fluoride, hydrogen sulfide, nitric acid, nitrogen dioxide, p-phenylene diamine, phosgene, and sulfur dioxide. As advertised, the Series 7100 continuous toxic gas monitors are capable of detecting concentrations as low as 1 ppb.
The British standard method for the determination of arsenic is disclosed in British Standards Publication BS4404 and is also referred to as the silver diethyldithiocarbamate procedure for the determination of arsenic.